1. Technical Field
The present invention relates to an optical filter, an optical filter module, and a photometric analyzer.
2. Related Art
A known optical filter extracts light having a specific wavelength from light having plural wavelengths. An example of such an optical filter is a tunable interference filter.
A tunable interference filter is an optical filter in which reflection films (optical films) formed on substrates oppose one another and a gap dimension between the reflection films is changed by an external force to transmit light having a wavelength corresponding to the gap dimension.
JP-A-1-300202 (see FIG. 1(b)), discloses a configuration in which a titanium oxide thin film layer, a silver thin film layer, and a protective film are sequentially stacked as a reflection film on a substrate. The protective film is provided for preventing deterioration due to sulfuration and humidity of the silver thin film layer because of exposure to the air for a long period.
However, the protective film according to JP-A-1-300202 is formed using an insulating material, and there is a problem that a charge is accumulated on the surface of the insulating material and the reflection film thus becomes charged.
Accordingly, in the tunable interference filter in which the reflection films are oppositely provided, a repulsive force or an attractive force is generated between the reflection films due to the charging of the reflection films. This causes a reduction in the accuracy of controlling the distance between the reflection films.